The present specification relates to the fabrication of integrated circuits. More specifically, the present specification relates to an optical technique to detect the termination of a dry etch or plasma etch process using the reflected or absorbed signal in absorbing regions of chemicals or surfaces exposed to the beam at process termination.
Scatterometry has been developed to characterize critical dimensions (CDs) of topographic integrated circuit (IC) structures of both photoresist before etch and circuit features in relief after etch. Scatterometry can include using a light beam over varying angles of to incidence with a broad band source that is typically in the spectral range of 230 nm to 850 nm and is used to illuminate a target area of 50 xcexcm to 100 xcexcm. The target area (scatterometry target) is not necessarily part of the IC and is typically in the scribe area of the wafer or other unused portion of the wafer. The wafer is cut in the scribe area to form IC chips. The target array includes a periodic array of the features at the minimum design rule which can represent the features in the integrated circuit. The features in the IC are more randomly distributed than the features in the periodic array and can be larger than the minimum critical dimension (CD).
The scatterometry target diffracts the light from the beam and the scattered signal is analyzed. The shape and size (CD) of the feature in the periodic array is determined. A reflectance curve defines diffraction behavior from the periodic array in the target area in a highly non-linear way. Typically, it is not analytically possible to determine the structure in the target area from the reflectance curve. One approach of conventional scatterometry is to model the reflectance curves as a set of library curve sets which have been shown to correlate to the actual geometries of the structures in the periodic array. The structure in the periodic array in turn relates to the CDs of minimum feature sets within the IC circuit being examined.
While scatterometry has been utilized to characterize the geometry of IC structures, it has not heretofore been used to detect end points or process termination in an etch chamber. Detection of process end points is important in the fabrication of IC devices. A method for detection of process termination could lead to tighter tolerances of device features from the processes in the etch machine. Such a method could lead to tighter tolerances between wafers or between batches due to tighter in situ control of etch processing.
As dimensions of IC devices continue to shrink, it becomes important to identify the process end points accurately and decrease the variation of the process. Thus, there is a need for a method of scatterometry with infrared radiation where the nature of the substrate, the quality of chemicals on the substrate of the integrated circuit wafer or products in the gaseous state above the substrate are determined and used to control the etch process. Yet further, there is a need for detection of any of the above by interaction of scattered infrared light from the substrate with the respective absorption bands of each species. The use of such a detection scheme allows greater control over the etching process than conventional methods.
Thus, there is a need to identify etch process end points using a method of scatterometry defined by the detection of the interaction of scattered infrared broad-band light with the absorption bands by either reflection from or transmission through solids or gases on or above the wafer. Further, there is a need to continuously detect species in the vapor or solid phase and be used either to terminate the process or modify the process in midpoint.
An exemplary embodiment relates to a method of detecting a process end point during etching in the fabrication of an integrated circuit. This method can include receiving a reference signal indicative of an intensity of a light source, collecting a reflection signal reflected off a surface of an integrated circuit wafer, and comparing the reference signal and the reflection signal to locate absorption bands. The absorption bands are indicative of a process end point.
Another exemplary embodiment relates to a method of using scatterometry to detect integrated circuit (IC) process end points in an etch chamber. This method can include reflecting a beam of light off of an integrated circuit surface, and detecting absorption bands using the reflected beam of light. The absorption bands indicate integrated circuit process end points.
Another exemplary embodiment relates to a system for fabricating an integrated circuit in which process end points are detected. This system can include an etching chamber configured to etch an integrated circuit wafer, a light source which projects light in the etching chamber, and a detector which detects a light beam reflected off a surface of the integrated circuit wafer. The detector compares the reflected light beam with a reference signal to locate absorption bands, which are indicative of a process end point.
Other principle features and advantages of the present invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims.